Field of the Invention
The present invention relates to a stirring member that comprises at least two blades and is able to be fastened to a rotation shaft.
The manufacture of numerous products requires a homogenizing, diluting, dissolving, reheating, etc. operation.
To this end, use is frequently made of mechanical stirrers having a rotary shaft, which are driven frequently by way of an electric motor, and are provided with a shaft and a stirring member or stirrer. The assembly is thus made up of a container, a product and a stirrer.
The present invention concerns the design of stirrers which are generally propellers or turbines that comprise a member known as a stirring member mounted on a rotation shaft.
A turbine is provided with straight blades at 90° to the vertical, but any member made up of straight blades, even ones positioned in an inclined manner, is customarily known as a turbine.
A turbine generates a radial flow that generates shear, dissipating energy.
A propeller is preferably formed by a steeply inclined portion of helical pitch of a curved or bent sheet.
A propeller produces an axial and methodical flow.
The rotation of the stirring member causes the liquid to be displaced, making it possible to carry out the desired operation, more or less effectively depending on the shape of the member, its size and the speed of rotation.
The rotation can also cause shear and dissipate energy in the liquid to be mixed.
Sometimes, these two phenomena are necessary, during a reaction, for the formation of an emulsion.
The invention deals more specifically with the case in which the aim is to minimize the losses of energy by shear in order to obtain a displacement of the liquid and the mixing thereof with small losses, this entailing increased efficiency.
In such a case, it is the use of a propeller that gives the best result. This is because these operations only require that the product is set in motion, i.e. a pumping flow.
The aim is to produce this flow with the least possible energy, and it is known that propellers consume less energy than turbines for an equivalent flow.
Description of the Related Art
In previous centuries, use was made only of turbines, which did not require a particular design; then, around a century ago, marine propellers, which are more efficient and less energy-consuming, were developed.
Two large families of propellers, which are represented by the patents U.S. Pat. No. 4,147,437 and FR 1 578 991, can be distinguished.
These two families of propellers are still used today, given their performance in relation to marine propellers.
However, in some markets, it proves difficult to use turbines, on account of the high power required and consequently the cost, or high-efficiency propellers.
This is because such a use is frequently considered to be too expensive, since the benefits of the high efficiency are not fully appreciated, only the investment cost actually being taken into consideration. The high efficiency is considered to be advantageous only for large machines, or when the cost of the energy is high or at least taken into account.
It is a difficult and/or lengthy, and thus costly, process to manufacture high-efficiency propellers, and it can only be carried out by special machines. This is because there are numerous technical problems on account notably of the thickness of the sheet and the curves that are tricky to obtain. It is not possible to have these propellers manufactured at another workshop or on another continent, for example, which results in high transportation costs.
Bent propellers already exist on the market, but these have a very specific shape with a bend at the blade corner so as to limit radial leakage. The improvement in efficiency was not the technical problem that the designers thereof intended to deal with.
There is therefore a need for a propeller that is easy to construct, i.e. without special material or particular skill, provides a good flow, which is the essential determining factor of stirring, but without consuming too much power as would be the case for a simple blade having a flat and inclined shape, which would actually result in high power, a large shaft and a great thickness of the blade and ultimately in an uncompetitive manufacturing cost.